Process for converting normally gaseous hydrocarbons into gasoline



F. E. FREY 2,170,367

MALLY GASEOUS HYDROCARBONS INTO GASOLINE Aug. 22, 1939.

PROCESS FOR CONVERTING NOR Filed May 11, 1957 mm m F x w m T E 5 II 1| 5 W K V c mm :JTIU N I mm mm I R l Al Al E M.MM.M ATTORNEYS.

Patented Aug. 22, 1939 PROCESS FOR CONVERTING NORMALLY GASEOUS HYDROCARBONS INTO GASO- LINE.

Frederick E. Frey, Bartlesville, Okla", asslgnor to Phillips Petroleum Company, a. corporation of Delaware Application May 11,1937, Serial No. 142,047

9 Claims.

This invention relates to the production of higher molecular weight hydrocarbons from lower molecular weight hydrocarbons, and more particularly to an improvement in the production of hydrocarbons in the gasoline range from normally gaseous hydrocarbons.

It is an object of my invention to produce gasoline of high quality from normally gaseous hydrocarbon mixtures containing unsaturated and 10 saturated hydrocarbons.

It is a further object of my invention to treat a hydrocarbon mixture containing normally gaseous unsaturated and saturated hydrocarbons in such a manner, that conversions are efiected ll under optimum conditions in separate steps or stages to form normally liquid products in the gasoline boiling range.

Still another object or my invention is to treat such a mixture as the foregoing inseparate steps or stages with a minimum of heating expense, and with a minimum of cooling between the steps, thereby obtaining a highly economical operation.

Further objects and advantages will become apparent from a consideration of the following discussion and disclosure.

It is known that normally gaseous unsaturated hydrocarbons may be converted to normally liquid hydrocarbons by treatment at elevated temperatures in the absence of catalytic bodies, both with and without high superatmospheric pressure, and they may be converted to normally liquid hydrocarbons at lower temperatures in the presence of certain catalysts. However, many catalysts also promote undesirable side reactions, or are more or less easily contaminated with impurities, and therefore non-catalytic processes have certain advantages. It is also known that normally gaseous saturated hydrocarbons may be thermally treated to produce more desirable hydrocarbon products, such as normally liquid hydrocarbons. Since the primary reactions which are involved in processes for treating saturated hydrocarbons are endothermic in nature and take place at appreciable velocities only at high temperatures, a great deal of energy is needed to heat such reactants to the high temperatures and to supply energy at these temperature levels which is taken up by these endothermic reactions. On the other hand, reactions involving the union of unsaturated molecules to other hydrocarbon molecules, be they unsaturated or saturated, are extremely exothermic in nature, and processes which convert hydrocarbon mixtures containing large quantitles of unsaturated hydrocarbons must be carried out with this in mind.

I have found that optimum yields of hydrocarbons boiling in the motor fuel range may be produced from normally gaseous hydrocarbon mixtures, which contain substantial amounts of unsaturates, in a process of extreme economy by the efiicient cooperation of steps as will now be described and disclosed. This process has special utility where large amounts of normally gaseous hydrocarbons of higher molecular weight than methane are available, as methane is difllcult to convert, and mixtures of such hydrocarbons require a minimum amount of heating and therefore of fuel for successful and practical operation. Normally gaseous hydrocarbons which are suitable as charge stock for my process should contain both saturated and unsaturated hydrocarbons, and are preferably deficient in methane. Such mixtures should not have less than about 20 or 25 per cent by volume of unsaturated'h bdrocarbons and preferably not more than about 60 per cent of unsaturated hydrocarbons. Such mixtures may be readily obtained in a modern oil refinery from a number of sources, such as gases produced in pressure oil-cracking, or from a vapor recovery plant which takes vapors from storage tanks of cracked gasoline, or from other similar sources as will be readily appreciated by one skilled in the art. As previously stated, the methane content should be low and it is desirable,

although not necessary that the content of propane and butanes be fairly high. For these reasons, it is of course understood that some sort of separation operation may need to be applied to such mixtures as just enumerated, in order to obtain a charge stock which may be treated with the highest degree of over-all economy.

In the operation of this invention, a hydrocarbon mixture such as just discussed is treated under a substantial superatmospheric pressure, which should be over 500 pounds per square inch and which may be as'much as 3000 pounds per square inch or even more, and at an elevated temperature in the range of 370 to 540 C. for such a time that optimum yields of higher molecular weight hydrocarbons in the gasoline boiling range are formed. Under these conditions a. major part of the unsaturated hydrocarbons will undergo conversion of the polymerization type forming higher molecular weight hydrocarbons as a product. It is to be understood that while a large proportion of such products are formed by polymerization involving only unsaturated hydrocarbons, under certain modes of operation a certain amount of the saturated hydroc'h-fbons will also be involved in the polymerization reactions, uniting with unsaturated hydrocarbons to form saturated hydrocarbons without any complete disjunction of hydrogen or of light hydrocarbons such as methane. In any case, this step of the process will be exothermic, and the latter part of the step may be carried out in a more or less heat-insulated zone. The eflluents of this zone will have a temperature very near the reaction temperature, and will consist of unreacted saturated hydrocarbons along with some small amounts of unreacted unsaturated hydrocarbons, and higher molecular weight materials formed, with little or no material with a molecular weight lower than that present in the original charge stock to this step.

According to this invention, the hot efliuents above mentioned are subjected to a separation without extensive cooling, whereby most or all of the higher molecular weight material is removed and the unreacted hydrocarbons, which require more drastic conversion conditions, are still at an elevated temperature and may be directly subjected to such conversion without an excessive amount of reheating. One method of conducting this separation is to wash or scrub ,the hot eiliuents under pressure with a heavy absorption oil which is at an elevated temperature which may approximate the temperature of the .eiiluents of this first conversion zone. Under the pressure which exists in this part of the system, most of the polymers formed will be taken up by the oil and be carried off with it to other separating means where the desired products maybe separated for further treatment and use. As a result of this manner of operating the unreacted material does not need to be reheated to any great extent, but only needs a comparatively small temperature increase or increment while retaining the advantages of being converted under more drastic conditions in the absence of the higher'molecular weight material produced in the first stage.

The temperatures in the second stepor stage should be above 540 C., and may be as high as 815" C. or more,- but preferably is between 565 and 675 C. As a result of the.pressure drop which results from the flow through the apparatus the pressure in this second step will be somewhat less than that in the first step, and will range from about 200 pounds per square inch to about 2500 or 2750 pounds per square inch or more depending to a certain extent upon the pressure in the first step. A pressure drop greater than that caused by flow through the apparatus may be used if desired, so that a relatively high pressure may exist in the first step, with a relatively low pressure in the second step. Under these conditions, the predominantly saturated hydrocarbon mixture is converted very economically to a maximum yield of hydrocarbons boiling in the gasoline range, without undue formation of tar and coke, and without excessive formation of lighter hydrocarbons. The eiiluents of this second step are introduced into separating means where a gasoline fraction is separated, and any unreacted hydrocarbons may be separated and recycled to the appropriate step if desired. Light fixed gases and tars may be discharged from the system as necessary.

My invention will be more clearly understood by a consideration of the drawing which forms a part of this specification, and which illustrates diagrammatically and partially in section one form and arrangement of apparatus in which my invention may be practiced. However, it is to be remembered that this illustrates only one embodiment of my invention, and the invention should not be limited to it.

One mode of practicing the process of my invention will now be described in connection with this drawing. A suitable hydrocarbon mixture, containing both saturated and unsaturated hydrocarbons such as has been previously described and discussed, is introduced through conduit l0 and is compressed by pump I l to a pressure not less than 500 pounds per square inch, which may be as much as 3000 pounds per square inch or more, and passes through conduit l2 to a preheating zone l3 and to zone l4, which are located in the convection and conduction part of a furnace I5 heated by any suitable means such as the burner illustrated. The stream passes from zone l4 through conduit IE, valve l1 and conduit I 8 to separator or scrubber l9, while valve 20 in conduit 2| and valve 22 in conduit 23, which are connected to reaction chamber 24, are closed. In such a case, zone I3 is a preheating zone and in zone l4 further heating with polymerizing reactions involving unsaturated hydrocarbons takeplace, forming higher molecular weight hydrocarbons in the gasoline boiling range, and the effluents of this zone pass directly to the separator or scrubber l9. However, it may be desirable to extend the time of these reactions with intimate mixing of large portions of the reactants; in which case valves 20 and 22 are opened and valve I1 is closed and the stream is allowed to pass into the insulated reaction chamber 24 from which it again enters conduit I 6 and continues as described. With such a: mode of operation, zone I4 will not need, to be as extended as in the former mode of operation, but will only serve to heat the reactants further, to initiate the reaction which takes place in chamber 24.

In either case the step involves exothermic reactions, even when conditions are quite favorable to the polymerization of unsaturated hydrocarbons with saturated hydrocarbons, as will be the case when reaction chamber 24 is so built and operated as to have the contents in pronounced turbulent circulation with intimate mixing of the stream from the zones in the furnace with partially reacted, more saturated contents. All these reactions involving polymerization of unsaturated hydrocarbons proceed at temperatures between 370 and 540 C. and preferably in the range of 425 to 510 C., for a period of time such that optimum yields of hydrocarbons in the gasoline boiling range are produced. These reactions are exothermic, and a slight general temperature rise or loss of heat, or both, may take place throughout the reaction zone The material passing from conduit l6 into conduit l8 and separator or scrubber l9 may be at or near the temperature of reaction, but a small amount of unavoidable heat loss, which may be augmented by some limited partial cooling, by means not shown, will occur. However, the total heat loss should be controlled, so that the temperature of the separator is not below 260 C. The upper practical temperature limit of the s separator is about 455 C. with a preferred operating temperature in most usual cases between 350 and 400 C. The separator I9 is preferably operated under approximately the same pressure as exists in the heating and reacting zones of this first step, although of course some pressure drop due to friction may take'place. These elevated temperatures and pressures allow higher molecular weight hydrocarbons to be separated from the lighter unreacted hydrocarbons without any great heat losses. One quite practical and advantageous method of doing this is to wash or scrub the material flowing into separator I8 from conduit It with a counter-current flow of heavy hydrocarbon oil of approximately the same temperature, the oil remaining liquid and dissolving or absorbing the heavier hydrocarbon products of this first stage of my process. The oil charged as absorbing or wash oil is liquid at the temperature used and under the pressures which exist. v

The separation may be efiiciently and economically done in the following manner. Oil pumped by pump 25 passes through conduit 26 and valve 21 to the separator 19. The oil pumped by pump 25 may already be at an elevated temperature, as will be explained, and may be further heated in heat exchanger 28, by counter current heat exchange with hot rich oil leaving the separator IS. A final increment of heat may be added by heating coil 29 in heating means 30, by opening valve 3| in conduit 32 and valve 33 in conduit 34 and closing valve 21. By proper manipulation of these valves the temperature of the oil entering the absorber may be accurately controlled.

Separator or absorber IS, in this particular case operates as a conventional absorber, except that the pressure of operation is generally quite high, generally near the operating pressure of the first conversion stage of the process, and the temperature is appreciably higher than is conventional, i. e., up to about 455 C. as has been described. Higher molecular weight hydrocarbons formed in my process and contained in the mixture passing through conduit 18 into the absorber will be absorbed or dissolved in the oil. The rich oil passes out through the conduit 36 and may pass through valve 31, heat exchanger 28, conduit 38 and reducing valve 38 to separator or flash tank 40. However, it may be desirable to pass all or a part of the rich oil through conduit 4| and valve 42 to conduit 38 and separator 48, in which case valve 31 will be closed or partially closed, as the case may be.

In this instance, the oil passing into separator 40 is at an appreciable superatmospheric temperature, and may have the pressure reduced by reducing valve 39 so that hydrocarbon products of the process absorbed by the oil in absorber l9 will be flashed oil in separator or flash tank 40. Flashed vapors will pass through conduit 43, .and may pass out of the system for further separation and treatment through valve 44, or they may pass through conduit 45 andvalve 46 to conduit 65 as will be described, valve 44 being closed. The flashed oil will pass through conduit 41, and may be discharged all or in part through valve 48, or all or part of the oil may pass through conduit 48 and valve 50 to conduit 51, whence it is charged to pump .25. Oil passing through valve 48 may be subjected to further separation and treatment as desired. Fresh absorbing oil may be introduced to the system through conduit and valve 52. Since the oil is flashed in chamber 48 .at an elevated temperature at approximately or not excessively less than the temperature of separator 18, the flashed oil will still ,be at an elevated temperature, so that only relatively small increments of heat will need to be added to the oil recycled before it is reintroduced into separator l9.

The lighter hydrocarbons leaving separator or absorber 18 through conduit 68 and valve 6| will predominantly saturated and preferably will be between 565 consist largely of unreacted hydrocarbons not absorbed by the oil, and will still be at an elevated temperature and a superatmospheric pressure.

or radiant part of the fur- I nace I5. .The hydrocarbon material passing through zone 62 will be heated and maintained at temperatures in excess of about 540 C., and which may be as high as 815 C. or more and and 675 C. The pressure in zone 62 will be somewhat lower than the pressure induced by pump ll, due to the friction of the system up to this point. If desired the pressure may. be further reduced by proper control of valve 6|, in which case separator l9 will operate under a higher pressure. It is evident that if it is desired to operate both the zone 62, with subsequent parts of the system, and .also separator l9 under a lower pressure, this may be effected by proper control of valves l1 or 22. In any event, the predominantly saturated hydrocarbonsentering zone or tube coil 62 will be subjected to endothermic conversion in this zone, whereby higher molecular weight hydrocarbons are formed in a manner well known in the art. The effluents of zone 62 pass through conduit 63, valve 64, conduit 65, and valve 66 to separating means 61, while valve 18 in conduit 1| and valve 12 in conduit 13, connecting reaction chamber 14 are closed. It may be desirable to continue the reactions, initiated and/or partially continued in zone 62, for a longer period of time by using an enlarged and insulated reaction chamber as illustrated at 14, in which case valves and 12 will be open and valve 64 closed, the effluents of the chamber re-entering conduit 63, and continuing their flow as described. In separating means 61 the material is divided into a gasoline .and heavier portion which is discharged by conduit and valve 16 for further separation and treatment, while lighter hydrocarbons pass through conduit 11 and valve 18. It may be necessary or desirable to cool the material introduced into separator 61 immediately before introduction thereinto by conventional means which are not illustrated.

All or a portion of the flashed vapors from separator 40 may also be introduced into separator 61, one method being to pass them through conduits 43 and 45 and valve 46 into conduit 65. In this manner the total products of the process may be removed through conduits 15 and 11.

If desired a certain amount of hydrocarbon material similar in composition to the mixture leaving separator l9 through conduit 68, may be introduced to the process through conduit 80 and valve 8|, having been compressed to the desired pressure by pump 82 .and passed through heat exchanger 83 in indirect countercurrent heat exchange with the hot eilluents of the secondstage of the process from zone 62 and which are passed through conduit 63 to conduit 65. It will be appreciated that the hydrocarbons in conduit 63 will be in considerably larger amounts than the hydrocarbons passing through conduit 80 and will be at an appreciably higher temperature than the hydrocarbons in conduit 68, so

A portion of the stream passing through conduit 65 may be passed through conduit 8! and valve 86 and compressed or boosted in pressure by pump 81 and passed through conduit 88 and valve 89 to conduit l8 and separator l8. This .aifords a convenient and economical method-of material containing both unsaturated and saturated hydrocarbons under a high pressure is heated to a relatively low temperature and undergoes exothermic conversion under conditions which are favorable to a maximum yield of hydrocarbons in the gasoline range, and with a minimum of tar and coke formation. These higher molecular Weight hydrocarbons are then removed without the excessive temperature reductions and heat losses in'common use in the art, and the now smaller quantities of material, which passed unconverted through the first step and still retain most of their sensible heat content, together with possible recycled or added hydrocarbons of similar composition and temperature, now need only relatively small increments of heat at these higher temperatures to convert them, forming further quantities of higher molecular weight hydrocarbons suitable for gasoline. Although the actual operation of countercurrent heat exchange is old, my invention is further novel in that it permits an extraordinary and unusually advantageous use to be made of this manner of heating. Oil charged to the absorber is in' the liquid phase and at an elevated temperature, and leaves the absorber at this elevated temperature and with absorbed or dissolved lighter hydrocarbons in it-under a'high pressure. These may be flashed ofi without further heat being added, unless small increments are desired when absorber I9 is operated in the lower part of the temperature range disclosed. The flashing of the oil may be carried out in one or more stages, instead of the single stage shown, as will be appreciated by those skilled in the art. The flashed oil will still be at an elevated temperature, so that only small increments of heat will need to be added to bring it back to the temperature of the absorber I9. Additional normally gaseous predominantly saturated hydrocarbons, charged through conduit are readily heated in heat exchanger 83 to the temperature of the material passing from separator l9 through conduit 60 by ably greater amount of the material in the conduit 83 and the higher temperature it possesses as it leaves the conversion zone of this high temperature step.

As one example of the operation of the process of my invention, a normally gaseous hydrocarbon mixture of the composition shown in Table I may be charged through conduit l0 and heated and converted under a pressure of 2200 pounds per square inch so that'the eflluents of the first reaction zone have a temperature of 475 C. and contain higher molecular weight hydrocarbons with the normally gaseous fraction containing 9 per cent unsaturates and 64' per cent reason of the consider-- propane and butanes, with some ethane and methane. The heavier hydrocarbons are absorbed in heavy oil without substantial reduction .in pressure or temperature, and the normally gaseous fraction is passed to the second heating and conversion zone, along-with similar added hydrocarbons. equal to 30 per cent of the total mixture which has been previously raised to the same temperature and pressure. The second zone is operated under a pressure of 1500 poundsper square inch at a conversion temperature of 650.

C., resulting in the production of gasoline boiling range hydrocarbons equal to 16 weight per cent of the efliuents of this step. These eflluents are subjected to conventional separating steps, and appropriateportions of, normally gaseous hydrocarbons are recycled through the process, material too light for reprocessing being used for fuel. Gasoline hydrocarbons are also separated from these eiliuents, and from the previously men- Although the preceeding discussion and description has outlined preferable modes of op eratlon, it will be understood that my invention will be practiced under varying conditions ac;- cording to the situation to be met, exact conditions for any particular case being easily determined by trial by one skilled in the art.

I claim:

1. A multistage process for the conversion of normally gaseous hydrocarbon mixtures containing both unsaturated and saturated hydrocarbonsinto normally liquid hydrocarbons in the gasoline boiling range, which comprises subjecting such a normally gaseous hydrocarbon mixture to a conversion temperature between 370 and 540 C. under a pressure per square inch for a period of time to produce an optimum yield of gasoline boiling range hydrocarbons, passing the eiliuents of said conversion without substantial reduction in pressure to a hot oil absorber and therein absorbing gasoline boiling range hydrocarbons in an absorption oil at a temperature less than 455 C. and greater than 260 C. to form a rich oil, flashing said rich oil at a lower pressure than exists in said absorber and removing gasoline boiling range hydrocarbons, adding a temperature increment to at least a portion of said flashed oil and returning said heated oil to said hot oil absorber, and subjecting the vaporous residue of said absorption to a conversion temperature between 540 and 815 C. under a pressure between 200 and 2750 pounds per square inch for a period of time to produce an optimum yield of gasoline boiling range hydrocarbons. 4

2. A multistage-process for the conversion of normally gaseous hydrocarbon mixtures containing such a, normally gaseous hydrocarbon mixture 7" between 500 and 3000 pounds tioned heavy absorption oil, as products of the process.

Table I v Component: Volume per cent CH4. 5 C2H4 -a 18 CzHe 11 CaHe 14 CaHa 17 C4Ha 6 C4H1o 29 Total in a first conversion stage to a conversion temperature between 370 and 540 C. under a pressure between 500 and 3000 pounds per square inch for a period 01 time to produce an pptimuni yield sorber and therein absorbing gasoline-boiling range hydrocarbons in an absorption oil at a temperature less than 455 C. and greater than.

260 C. and removing said absorption oil and absorbed hydrocarbons from the process, subjecting the vaporous residue 0! said absorption to a conversion temperature between 540 and 815 C. and under a pressure between 200 and 2750 pounds per square inch for a period of time to produce an optimum yield 01 gasoline boiling range hydrocarbons and introducing a portion of the eiiiuents of said high temperature conversion stage to said hot oil absorber.

3. A multistage process for the conversion of normally gaseous hydrocarbon mixtures containing both unsaturated andsaturated hydrocarbons into normally liquid hydrocarbons in the gasoline boiling range, which comprises subjecting such a normally gaseous hydrocarbon mixture in a first conversion stage under a pressure between 500 and 3000 pounds per square inch to a conversion temperature between 370 and 540 C. for a period of time to produce an optimum yield of gasoline boiling range hydrocarbons, passing the efliuents of this first conversion stage without any substantial reduction in pressure to a hot oil absorber operated at a temperature between 260 and 455 C. and therein separating gasoline boiling range hydrocarbons at an elevated temperature and removing said hydrocarbons from the process, subjecting the remaining eiiluents of said first conversion stage without any increase in pressure in a second conversion stage under a pressure between 200 and 2750 pounds per square inch to a conversion temperature between 540 and 815 C. for a period of time to produce an optimum yield of gasoline boiling range hydrocarbons, and separating said hydrocarbons so produced from the eilluents of said second conversion stage.

4. A multistage process for converting normally gaseous hydrocarbons within the gasoline boiling range, which comprises passing a normally gaseous hydrocarbon mixture, substantially free of methane and containing between and 60 per cent by volume of unsaturated hydrocarbons, under a pressure of between 500 and 3000 pounds per square inch to a first conversion stage and maintaining therein a temperature between 370 and 540 C. whereby gasoline boiling range hydrocarbons are produced from unsaturated hydrocarbons, passing the eifluents of said first conversion stage to a hot oil absorber without substantial reduction in pressure and'at a temperature between 260 and 455 C., introducing into said absorber an absorption oil at an elevated temperature countercurrent to said ei'fluents whereby gasoline boiling range hydrocarbons are removed from said eiliuents at a temperature between 260 and 455 C. and removing said absorption oil and absorbed hydrocarbons from the process, passing unabsorbed effluents of said first conversion stage under a pressure between 200 and 2750 pounds per square inch to a second conversion stage and maintaining therein a conversion temperature between 540 and 815 C. whereby gasoline boiling range hydrocarbons are produced by thermal conversion of lower molecuvture between 370 and 540 lar weight saturated and removing from theeiiiuents of said second conversion stage the gasoline boiling rangehydrocarbons so produced.

.5.- A cooperative multistage process for theconversion of. normally gaseous hydrocarbons intonormally liquid gasoline boiling ran e hydrocarbons, which comprises passing a normally 88s ous hydrocarbon mixture substantially free of methane and containing between 20 and 80 per cent by volume of unsaturated hydrocarbons under a pressure or between 500 and 3000 pounds per square inch to a first conversion stage wherein a temperature increment. is added and a conversion temperature between 370 and 540 C. is maintained whereby normally gaseous unsaturated hydrocarbons react producing gasoline boiling range hydrocarbons, passing the emuents of said first conversion stage to a hot oil absorber without substantial reduction in pressure and temperature,. introducing into'said absorber an absorption oil at an elevated temperature, operating said absorber at a temperature between 260 and 455 C. whereby gasoline boiling range hydrocarbons are absorbed in said oil and removing said absorption oil and absorbed hydrocarbons from the process, passing unabsorbed efliuents of said first conversion zone still at an elevated temperature and a pressure between 200 and 2750 pounds per square inch to a second conversion zone wherein a second temperature increment is added and a conversion temperature between 540 and 815 C. is maintained whereby normally gaseous saturated hydrocarbons are converted into an optimum yield of normally liquid hydrocarbons in the gasoline boiling range, passing the eiiiuents of said second conversion zone to separating means and therein removing said gasoline boiling range hydrocarbons so produced.

6. A process for the conversion of normally gaseous hydrocarbon mixtures containing saturated and unsaturated hydrocarbons into nor-. mally liquid hydrocarbons of the gasoline range, which comprises subjecting a normally gaseous hydrocarbon mixture containing unsaturated and saturated hydrocarbons to a first thermal conversion step under a pressure between 500 and 3000 pounds per square between 370 and 540 C. for a period of time to effect an optimum yield of normally liquid hydrocarbons, separating the said normally liquid hydrocarbons from unreacted normally gaseous hydrocarbons at a temperature between 260 and 455 C., and at a pressure not greater than that of said first step and greater than that of the second conversion step hereinafter recited, and

subjecting said normally gaseous hydrocarbons.

inch at a temperature 7. A process for the conversion of normally i gaseous hydrocarbon mixtures containing saturated and unsaturated hydrocarbons into normally liquid hydrocarbons of the gasoline range, which comprises subjecting a normally gaseous hydrocarbon mixture containing unsaturated and saturated hydrocarbons to a first thermal conversion step under a pressure between 500 and 3000 pounds per square inch at a tempera- C. fora period of time to effect an optimum yield ofnormally liquid hydrocarbons, separating the said normally-1 liquid hydrocarbons from vunreacted normally gaseous hydrocarbons at a temperature between 260 and 455 0., and at a pressure not greater than that of said first step and greater than that of the second conversion step hereinafter recited, mixing with said unreacted normally gaseous hydrocarbons a normally gaseous hydrocarbon mixture of similar composition and at approximately the same temperature and pressure, subjecting said normally gaseous hydrocarbons to asecond-thermal conversion step under a. pressure less than that/maintained in said first conversion step and in excess of 200 pounds per square inch and at a, temperature between 5 40.and 815 C. for a period of time to effect an optimum yield of normally liquid hydrocarbons.

8. An improved multistage process for the con version of normally gaseous hydrocarbon mixtures containing unsaturated and saturated hydrocarbons into hydrocarbons in the gaseoline range, which comprises first converting a normally gaseous hydrocarbon mixture containing unsaturated and saturated hydrocarbons at a temperature more than 370 and less than 540 C. and a pressure between 500 and 3000 pounds per square inch for a period of timeto produce optimum yields of gasoline boiling range hydrocarbons without excessive tar and coke formation, scrubbing said mixture with a heavy oil at a temperature between 260 and 455 C. and at a pressure not greater than that of said first step and greater than that of the second conversion step hereinafter recited, to remove higher molecular weight hydrocarbons therefrom, and subjecting the remainder of the resulting mixture to a second conversion at a temperature between 540 and 815 C. and Without any increase in pressure under a pressure less than that in the first conversion step but greater than 200 pounds per square inch for a period of time to produce optimum yields of gasoline boiling range hydrocarbons without excessive tar and coke formation.

9. In a process for the conversion of a normally gaseous hydrocarbon mixture containing both saturated and unsaturated hydrocarbons into hydrocarbons in the gasoline boiling range, the steps which comprise passing a normally gaseous hydrocarbon mixture, consisting predominantly of hydrocarbons of three and four carbon atoms per molecule and containing between 20 and per cent by volume of unsaurated hydrocarbons, under a' pressure between 500 and 3000 pounds per square inch to a first conversion stage and maintaining therein a temperature between about 425 and 510 C. whereby unsaturated hydrocarbons react forming hydrocarbons having higher molecular weights and in the gaso- -line boiling range, passing the eflluents of said first conversion stage to a hot oil absorber under a pressure intermediate the pressure maintained in said first conversion stage and the pressure maintained in a second conversion stage and at a temperature between 260 and 455 0., introducing into said absorber an absorption oilv at an elevated temperature and pressure countercurrent to said efliuents whereby gasoline boiling range hydrocarbons are removed from said effluents at a temperature between 260 and 455 C. and removing said absorption oil and absorbed hydrocarbons from the process, passing unabs'orbed effluents of said first conversion stage without any increase in pressure and at a pressure between 200 and 2750 pounds per square inch to a second conversion stage and maintaining therein a conversion temperature between about 565 and 675 C. whereby normally gaseous saturated hydrocarbons are converted into an optimum yield of normally liquid hydrocarbons in the gasoline boiling range, and separating from the efiiuents of said second conversion zone hydrocarbons in the gasoline boiling range so produced.

FREDERICK E. FREY. 

